PADGEM protein in human erythroleukemia cells
E Yeo, BC Furie and B Furie
Division of Hematology-Oncology, New England Medical Center, Boston, MA
02111.
PADGEM protein, a platelet alpha granule membrane glycoprotein with a
molecular weight of 140,000, is translocated to the plasma membrane during
granule secretion and platelet activation. PADGEM protein is expressed on
the surface of activated platelets but not on the surface of resting
platelets. Human erythroleukemia (HEL) cells contain platelet alpha
granule-like organelles, alpha granule proteins, and express platelet
membrane glycoproteins GPIIb/IIIa and GPIb. We demonstrate that HEL cells
express a protein that has a molecular weight identical to that of PADGEM
and binds to anti-PADGEM antibodies. The exposure of HEL cells in culture
to dimethylsulfoxide (DMSO) increased the number of cells expressing
PADGEM. Fluorescence activated flow cytometric analysis demonstrated an
increase in mean surface expression of PADGEM in DMSO-exposed cells
compared to noninduced cells. Total cell content of PADGEM was increased
5.3-fold after DMSO exposure, as determined by radioimmunoassay. Direct
binding experiments with the monoclonal anti-PADGEM antibody KC4
demonstrated specific, saturable, and time-dependent interaction of KC4
with HEL cells. A Kd of 7 nM was estimated. There were 14,000 surface
binding sites per cell in noninduced cells and 24,000 surface binding sites
per cell in DMSO- induced HEL cells. Surface expression of PADGEM protein
on HEL cells was not increased with platelet agonists, including thrombin,
epinephrine, ADP, nor cytokines, including IL-1, IL-2, tissue necrosis
factor. The presence of PADGEM protein in HEL cells should facilitate the
elucidation of the function of PADGEM protein.
Volume 73,
Issue 3,
pp. 722-728,
02/15/1989
Copyright © 1989 by The American Society of Hematology
